The handling of large sheets of heavy material, such as float glass or the like, is effected in a variety of different ways. In many applications, the stacking or moving such sheets of material is accomplished manually by two or more production workers. Manual handling of material, such as sheets of float glass, however, is difficult repetitive work; and substantial care must be exercised to prevent the breakage of glass during handling and stacking of float glass sheets.
In window manufacturing plants, large sheets of float glass, typically on the order of eleven feet by fourteen feet (11'.times.14') are stored on edge on support apparatus or bucks which cause the individual sheets to be inclined in a plane 5.degree. to 15.degree. from vertical. A large number of sheets are stored on such support apparatus or bucks, leaning against the support apparatus. The top or front sheet of the stack typically is removed from the stack and is placed on a horizontal work table or platform. Sometimes this is done manually by pivoting the sheets about the bottom edge and allowing them to free-fall onto a horizontal surface. The glass sheet then is cut into the desired smaller sizes for use in window fabrication and the like. Because the sheets are relatively heavy, on the order of four-hundred fifty pounds (450 lbs.) or more, manual movement of the sheets in this manner is difficult, and periodically a sheet is dropped and broken.
In some plants, the sheet removing operations for moving the sheets of glass from the near vertical stored position to a horizontal position is carried out by workers who manipulate a frame equipped with vacuum cups which attach to the glass. The glass sheets must be carefully lowered into position and the frame adds to the weight being manipulated by the workers.
Automatic equipment for handling large sheets of float glass in glass manufacturing plants has been developed. Three patents which disclose vacuum operated glass handling devices primarily used in a manufacturing plant to lift horizontal sheets of glass from a conveyor belt to stack them in a vertical stack, are the U.S. Pat. Nos. to Wheat #3,178,041; Miller #3,679,076; and Klaus #4,093,083. All three of these patents disclose devices which hold the glass in place by means of suction apparatus throughout the entire movement of the glass sheet from the horizontal position to the vertical or near vertical storage position. In view of the heavy weight of large glass sheets, strong vacuum systems and massive mechanical and hydraulic machinery is necessary.
Three other patents which disclose systems for moving sheets of glass from a vertical stack and placing them on a horizontal surface, are the U.S. Pat. Nos. to Langhart #3,126,108; Werner #4,444,537; and Pascale #4,750,854. These patents are similar to the three patents mentioned above, except that the vacuum systems are used to move the glass first from a vertical position to place it in a horizontal position. The entire movement, however, is handled by a mechanical device which holds the glass in place by means of a suction apparatus throughout the movement from one position to another As in the case of the three patents mentioned above, the devices of these patents would require extremely heavy duty mechanical structures and very strong vacuum systems if they were to be used for handling large sheets of float glass (for example 11'.times.14'.times.1/8" or 1/4" thick).
Other prior art exists for utilizing automatic or semiautomatic equipment employing vacuum suction cups for moving sheets of glass into place in a factory or on a construction site. Such devices, however, employ the vacuum apparatus to hold the glass in place throughout the entire movement and placement of the glass, so that the vacuum apparatus must be capable of holding the weight of whatever size glass sheet is handled by it.
It is desirable to provide a method and apparatus for handling sheet material, particularly large sheets of float glass, to move such sheets of material from a vertical position to a horizontal position in a simple and effective manner without requiring heavy duty equipment to accomplish such a purpose.